Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment, as examples. Semiconductor devices are typically fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductive layers of material over a semiconductor substrate, and patterning the various material layers using lithography to form circuit components and elements thereon.
The semiconductor industry continues to improve the integration density of various electronic components (e.g., transistors, diodes, resistors, capacitors, etc.) by continual reductions in minimum feature size, which allow more components to be integrated into a given area. These smaller electronic components also require smaller packages that utilize less area than packages of the past, in some applications.
Thus, packages such as wafer level packaging (WLP) have begun to be developed, in which integrated circuits (ICs) are placed on a carrier having wiring for making connection to the ICs and other electrical components. In the WLP process, grinding may be used. In the formation of fan-out chip scale packages, device wafers may be sawed, and the known-good-dies are selected and attached onto a carrier, with the known-good-dies spaced apart from each other. The known-good-dies include copper posts for the formation of fan-out connections. A molding compound is then filled into the space between and over the known-good-dies to form a fan-out wafer. After the curing of the molding compound, a grinding process may be performed to remove the portions of the molding compound and other dielectric materials over the copper posts. After the copper posts are exposed, electrical connections may be made to connect to the copper posts, so that the connections to the fan-out wafer are extended into an area larger than the area of the known-good-dies.
Since the layers that are subject to the grinding are often thin layers, accurately stopping the grinding process at the right time is vital to the yield of the integrated manufacturing process. For example, in the manufacturing of the fan-out wafer, the grinding needs to be stopped when the copper posts in substantially all known-good-dies throughout the fan-out wafer are fully exposed, and substantially no over-grinding occur. In the existing grinding technology, a gauge is used to detect the total thickness of the fan-out wafer during the grinding process. When the total thickness is reduced to a pre-determined value, it is assumed that the copper posts are fully exposed. This detection method, however, is inaccurate, and may result in yield loss.
Thus, an improved grinding process is needed to increase the yield of the packaging process.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.